1. Field of the Invention
The present invention relates to a process for producing a polycarbonate resin foamed blow-molded article by blow molding a foamed parison, and to a polycarbonate resin foamed blow-molded article.
2. Description of Prior Art
Because a polycarbonate resin (hereinafter occasionally referred to as “PC resin”) has much higher melt viscosity at near its foaming temperature and requires an extremely higher extrusion pressure as compared with other resins such as polystyrene, it has been difficult to extrude and foam the PC resin. Moreover, because the melt tension of a PC resin is much smaller than other resins such as polystyrene, cells are apt to be broken during the growth thereof. Therefore, the obtained PC resin extruded foamed product shows only an insufficient expansion ratio and the cells thereof are not uniform in size. In particular, the PC resin foamed blow-molded article has an expansion ratio of as low as about 1.3. It has not been possible to obtain a PC resin foamed blow-molded article having such a high expansion ratio as achieved in the case of a polystyrene or a polyethylene resin.
In this circumstance, Japanese unexamined patent publication No. JP-A-2000-033643 proposes a method in which a PC resin having a branched structure and a specific melt tension is extruded to form a foamed parison. By blow-molding the parison, a PC resin foamed blow-molded article having an acceptable expansion ratio is obtainable.
Japanese unexamined patent publication No. JP-A-2008-144084 proposes a method in which a modified PC resin obtained by modifying a commercially available branched PC resin with a branching agent is extruded through a die with a large area to obtain a foamed board that has a high expansion ratio and a large sectional area and that shows a high compression strength even at both side end regions in the width direction thereof.